The euro was traded at $1.2512 around 2100 GMT, dipping from $1.2562 at the same time Thursday.
The European currency slipped to 98.43 yen from 98.59 yen late Thursday.
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The dollar firmed against the Japanese unit, to 78.67 yen from 78.47 yen.
"With positive risk sentiment fading somewhat at the end of the week, the US dollar is gaining across the board," said Vassili Serebriakov, currency strategist at Wells Fargo Bank.
"European headlines are contributing to a more cautious mood," he said, citing a report suggesting that the ECB may wait for the German Constitutional Court ruling on a rescue fund, the European Stability Mechanism, before announcing the details of its bond purchase plans.
"There is also considerable nervousness surrounding the ongoing talks between Greece and European leaders, with few significant announcements made at this stage," he added, referring to crisis talks over debt-laden Greece's performance under an international rescue program.
Traders weighed a report that the ECB could set yield targets to get eurozone sovereign borrowing rates under control if it starts buying up sovereign debt to help end the region's debt crisis.
Bank of New York Mellon analyst Michael Woolfolk said that ongoing news reports surrounding a potential Greek exit from the eurozone were "expected to continue to trump economic developments, with the euro vulnerable to any increased likelihood of an exit."
The dollar firmed against the Swiss currency, to 0.9595 francs, compared with 0.9559 francs late Thursday.
The greenback also strengthened against the British pound, which slipped to $1.5803 from $1.5858.
